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The arrests were based on information from a former officer who was also charged

A band of rogue Philadelphia police officers allegedly held a drug suspect over the balcony railing of his 18th-floor apartment as an interrogation technique, federal prosecutors say.

In another instance, according to prosecutors, the six officers allegedly kidnapped a drug suspect and kept him in a hotel room for days while threatening his family.

In what Philadelphia's police commissioner described as one of the worst cases of corruption, the six officers were arrested Wednesday on a range of charges, including conspiracy, robbery, extortion, kidnapping and drug dealing. The case centers on a six-year scheme in which they allegedly pocketed $500,000 in drugs, cash and personal property, including Rolex watches and designer suits, authorities said.

Attempts to contact the officers for comment were unsuccessful. It was unclear whether they have hired lawyers.

The arrests came after a nearly two-year joint investigation by the FBI, federal prosecutors and Philadelphia Police internal affairs unit, said U.S. Attorney Zane David Memeger said. The suspects were named in a 42-page indictment unsealed on Wednesday.

"I have been a police officer for more than 40 years, and this is one of the worst cases of corruption that I have ever heard," Police Commissioner Charles Ramsey told reporters.

Memeger said the officers allegedly engaged in an array of criminal activities, including beatings, threats to shoot a suspect, entering homes without warrants for the purpose of stealing money and drugs, and the distribution of narcotics.

"The reprehensible conduct alleged to have been committed by the six charged officers tarnishes the badge held by the thousands of officers who currently serve -- and have previously served -- this city with distinction," Memeger told reporters.

The officers often filed false police reports to conceal their activities, Memeger said.

Investigators used information provided by Jeffrey Walker, a former member of the narcotics unit, to build a case against the officers, Ramsey said.

In May 2013, Walker was arrested on charges of robbery, extortion and using his position as a police officer to commit criminal acts, according to a criminal complaint. Walker pleaded guilty to robbery charges and will be sentenced on November 4, according to Patty Hartman, a spokeswoman for the U.S. Attorney's Office. He faces up to 10 years in prison.

Investigators corroborated information provided by Walker to indict the six officers, authorities said.

The six officers were pulled off the street and removed from narcotics investigations after the district Attorney's Office informed the police commissioner that their testimony could no longer be used in cases, Ramsey said.

The officers were not fired at the time in an effort to avoid jeopardizing the ongoing investigation, Ramsey said.

The Philadelphia District Attorney's Office is reviewing previous convictions involving the six officers, according to a statement. The office said it has no open cases involving Liciardello, Reynolds, Spicer, Betts and Speiser at this time. Cases involving Norman will be reviewed for the relevant period.

If convicted, the officers could face between 40 years and life in prison, according to Memeger.